Treating a sprain in a U.S. hospital can cost $4 to $24,000, making a trip to the emergency room financially risky for uninsured patients, researchers said. A study found wide variety between the lowest and highest charges for 10 common conditions, highlighting the unpredictability of health-care costs. Bills were $50 to more than $73,000 for urinary tract infections, $15 to $17,797 for headache care and $29 to $29,551 for intestinal infections.